This invention relates to wire grids and methods for making the same. More particularly, this invention is directed to parallel-wire grids used in ionization chambers of the parallel-plate type. Such chambers have a grounded cathode which is coated with a radioactive material, and an anode to which a positive potential is applied. The chamber, which is pressurized with a gas such as argon, acts as a neutron detector in that neutron bombardment of the cathode releases fission fragments which ionize the gas. Ion products accelerated toward the anode create a measurable electrical current which is proportional to the frequency of ionization events occuring within the chamber. In order to control the migration of negative ions to the anode, a positively charged parallel-wire grid is positioned in the ion path between cathode and anode in a direction perpendicular thereto. Such grids consist of a number of spaced-apart parallel wires secured to a conductive frame. Prior art grids were typically formed by individually welding each wire of the grid to a frame member. This is usually a difficult, time-consuming process in that each wire added to the frame changes the forces applied to the frame, and often the configuration thereof, causing a change in the tension of previously secured wires. The spacing between the cathode and anode can be increased, and the chamber can be pressurized to higher level if, for a given transparency (ratio of total wire surface area to inter-wire spacing), the interwire spacing could be reduced. This, in turn, would require an even greater accuracy in uniformly spacing adjacent wires during assembly.
It is therefore an object of the present invention to provide an inexpensive parallel-wire grid, having improved accuracy of wire spacing.
It is a further object of the present invention to provide a simplified method for making a parallel wire grid.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.